Many experimental techniques (e.g., small-angle x-ray scattering) utilize highly concentrated beams of electromagnetic radiation (e.g., x-rays) directed at a sample. When x-rays interact with the sample, a portion of the x-rays are scattered or diffracted by the sample (e.g., x-rays are diffracted in protein crystallography). These scattered or diffracted x-rays travel to a detector (e.g., a Pilatus detector or a silicon pixel detector). Experimenters use the pattern of scattered or diffracted x-rays captured by the detector to obtain information about the sample.
Much of the x-ray beam, however, passes through the sample without interacting with the sample. This portion of the x-ray beam also travels toward the detector. If this unscattered portion of the beam is allowed to interact with the detector, it may overwhelm and/or slowly damage the detector and the scattered x-rays may not be observable. In order to prevent this, a beam stop can be placed between the sample and the detector to prevent the unscattered x-rays from hitting the detector. In order to be fully effective and useful, a beam stop should be as small as possible to prevent obstruction of the scattered x-rays and dense enough to absorb the unscattered x-rays. FIG. 1 shows an example of a schematic illustration of a setup at a beamline (e.g., at a synchrotron light source), including a sample, a detector, and a beam stop.
The unscattered portion of the x-ray beam, however, does carry information about the intensity, size, and position of the x-ray beam. If the unscattered x-rays could be characterized, in real time, during an experiment, such information potentially would be useful to experimenters.